Enzyme treatment of glucans

ABSTRACT

β-(1-6)-Glucanase treatment of glucan from yeast cells, pure or feed grade, especially yeast from the family Saccharomyces and particularly  Saccharomyces cerevisiae , provides a novel glucan product suitable for use in enhancing the stimulation of host animal immune systems. Solubilization of such yeast cell glucan is further disclosed to extend the usefulness of yeast cell glucan as an adjuvant.

This invention relates to the structural modification of yeast glucans,especially but not exclusively from the family Saccharomyces, by usingβ-(1-6)-glucanase, and the use of such modified glucans in vaccine andanimal feed formulations.

BACKGROUND OF THE INVENTION

It is known from European Patent Application Ser. No. 91111-143.3(Publication No. 0466031 A2) that the immune system of aquatic animalscan be stimulated through the administering of an effective amount of ayeast cell wall glucan. It is further known that the effect of vaccineson such aquatic animals can be enhanced by the administering of aneffective amount of such yeast cell wall glucan along with the vaccineantigens.

Such glucan compositions are particulate glucans such as that derivedfrom the yeast Saccharomyces cerevisiae. Such particulate glucans aremacromolecular and are comprised of a chain of glucose units linked byβ-(1-3)- and β-(1-6)-linkages, said glucan being a brancedβ-(1,3)-glucan having β-(1,3)-linked and β-(1,6)-linked chains therein.

Such particulate glucans are provided by KS Biotec-Mackzymal under thebrand “MacroGard” and are potent activators of the macrophage/monocytecell series. Thus such particulate glucans have a profound effect on theimmune system.

While the particulate glucan derived from Saccharomyces cerevisiae isrecognized to have a variety of beneficial effects on fish and otheranimals, the use of the glucan in the particulate and thus insolubleform is limited.

In addition it is now believed that the presence of β-(1-3)-branchescontribute to the desired pharmaceutical benefits to be obtained fromparticulate glucan.

Accordingly a system whereby the β-(1-3)-linked branches are made morereadily available in the glucan would be highly desirable.

SUMMARY OF THE INVENTION

In accordance with the present invention it has been discovered that bytreating the particulate glucan derived from yeast organisms, especiallyof the family Saccharomyces, and particularly Saccharomyces cerevisiae,with a β-(1-6)-glucanase, there is obtained a modified particulateglucan which is characterized by its enhanced activity in effectingstimulation of the immune system.

Thus in one embodiment of the present invention there is provided anovel β-(1-3)-glucan from yeast which is characterized by its enhancedability to stimulate the immune system of fish and other animals.

In another embodiment of this invention there is provided a novelprocess for the production of β-(1-3)-glucan from yeast having enhancedpharmaceutical activity.

In another embodiment of this invention there is provided a novelsolubilized β-(1-3)-glucan from yeast which is useful for enhancing theactivity of veterinary vaccines.

In still another embodiment of the present invention there is provided anovel feed grade glucan composition which is useful as an ingredient inconventional animal feeds.

Other embodiments and advantages of this invention will be apparent fromthe following specifications and claims.

Process for Preparation of β-(1-6)-glucanase Treated Glucan(“MacroGard”).

“MacroGard” brand glucan is derived from Saccharomyces cerevisiae asdisclosed in European Application Ser. No. 91111143.3. While such glucanis known to stimulate the immune system of fish, according to apreferred embodiment of the present invention, its activity is enhancedby the treatment thereof with a β-(1-6)-glucanase.

Such glucanase treatment of the glucan is carried out by suspending theglucan particle in a buffered medium at a pH in the range of about 4 toabout 8 and at a temperature in the range of from about 20 to about 50°C. Suitable buffered media are those selected from the group consistingof sodium acetate, ammonium acetate and sodium-potassium phosphate.Presently preferred buffer solutions are sodium acetate or ammoniumacetate. Enzymatic degradation of the glucan is commenced by theaddition of the β-(1-6)-glucanase to the buffered medium.

β-(1-6)-glucanases which are suitable for the modification of yeastglucan in accordance with the present invention are those obtained froma microorganism selected from the group consisting of Trichodermalongibrachiatum, Trichoderma reesei, Trichoderma harzianum, Rhizopuschinensis, Gibberella fuiikuroi, Bacillus circulans, Mucor lilmalis, andAcinetobacter. Of these a presently preferred glucanase is that obtainedfrom Trichoderma harzianum.

The amount of β-(1-6)-glucanase employed for treatment of the glucan isnormally in the range of from 1 to 50 U per g of glucan.

Enzymatic degradation is terminated by heating the reaction mixture to atemperature in the range of 80 to 100° C., preferably for a time in therange of 2 to 10 min. Other ways to stop the enzyme degradation are,e.g. by adding proteases or inhibitors to the reaction mixture.

Alternatively the enzyme may be simply removed by washing. The washedparticles are then resuspended in water with the addition of abactericide such as 0.3% formalin (v/v) and stored at a temperature ofabout 4° C.

The resulting enzyme treated glucan can be characterized as a branchedβ-(1-3)-glucan with β-(1-3)-linked sidechains being attached by aβ-(1-6)-linkage and being essentially free of β-(1-6)-linked chains. Inthis connection the phraze “β(1-6) chains” is meant to include branchesof more than 1 β(1-6)-linked glucose units. The β-(1-6)-glucanase enzymecleavage ensures that most chains of more than 4 β-(1-6)-bound glucoseunits are cleaved off.

To further enhance the utility of the glucan, it is subject tosolubilization. Such solubilization treatment is generally carried outat a temperature in the range of about from 70 to 90° C. for a period offrom about 30 to 60 min in the presence of a solubilizing agent. Apresently preferred solubilizing agent is formic acid. Followingsolubilization the solubilizing agent is removed and the resultingglucan is boiled in distilled water.

In practicing the present invention glucan can be first enzyme treatedand then solubilized or conversely be solubilized and then enzymetreated.

In accordance with another embodiment of this invention there isprovided a β-(1-6)-glucanase treated feed grade glucan from yeast, e.g.Saccharomyces cerevisiae. Such feed grade glucan can be obtained byfirst contacting the yeast cell wall with an aqueous alkaline solutionunder conditions to effect the extraction of proteins and lipidstherefrom. Generally such extraction is carried out at a temperature inthe range from about 50 to 80° C. for about 2 to 8 h. A presentlypreferred alkaline extraction agent is sodium hydroxide. Followingextraction, the cell walls are recovered from the aqeous alkalinesolution and washed to remove solubilized cell wall componentstherefrom. The washed yeast cell wall are then neutralized by treatmentwith an acid such as phosphoric acid. Thereafter the neutralized washedglucan is pasteurized and then dried.

Suitable enzymes for treatment of the feed grade glucan are those usefulin treating the high purity glucan.

The enzyme treated feed grade glucan is prepared by contacting theglucan with a β-(1-6)-glucanase in the same manner as that employed tothe enzyme treatment of the glucan particulate. The β-(1-6)-glucanasetreated feed grade glucan of this invention is useful in animal feedformulations.

The following examples are presented for purposes of illustration of theinvention.

EXAMPLE 1

This example provides the protocol used to obtain an immunostimulatoryglucan particle suitable for utilization in the practice of the presentinvention.

500 g of dry Saccharomyces cerevisiae was suspended in 3 l of 6% aqueousNaOH solution. This suspension was then stirred overnight at roomtemperature. After stirring the suspension was centrifuged at 2000×g for25 min. The supernatant was discarded and the insoluble residue was thenresuspended in 3 l of 3% NaOH and incubated for 3 h at 75° C. followedby cooling the suspension overnight. The suspension was then centrifugedat 2000×g for 25 min and the supernatant was is decanted. The residuewas then resuspended in 3% NaOH, heated and centrifuged as previouslydescribed.

The insoluble residue remaining was then adjusted to pH 4.5 with aceticacid. The insoluble residue was then washed with 2 l of water threetimes and recovered by centrifuging at 2000×g for 25 min. after eachwash (the supernatant was poured off). The residue was then suspended in3 l of a 0.5 M aqueous acetic acid. The suspension was heated for 3 h at90° C. The suspension was then cooled to room temperature. Aftercooling, the insoluble residue was then collected by centrifuging at2000×g for 25 min. This treatment (from adjusting to pH 4.5 tocollecting the cooled residue) was repeated 6 times.

The insoluble residue was then suspended in 3 l of distilled water andstirred for 30 min at 100° C., then cooled and centrifuged at 2000×g for25 min. The supernatant was discarded. The insoluble residue was washedin this manner 4 times. The residue was next suspended in 2 l of ethanoland heated at 78° C. for 2 h. This wash with ethanol was repeated 4times. The residue was then washed 4 times with 3 l of distilled waterat room temperature to remove the ethanol, thereby providing asuspension of desired glucan product.

EXAMPLE 2

This example provides the protocol to obtain glucan particlesessentially free of β-(1-6)-linked chains with the use ofβ-(1-6)-glucanase isolated from Trichoderma harzianum.

200 mg of glucan particles prepared in accordance with Example 1 weresuspended in 40 ml 50 mM ammonium acetate buffer, pH 5.0, together with10 U of β-(1-6)-glucanase at 37° C. for 6 h with constant stirring. Theenzymatic degradation of the glucan particles was ended by heating thesuspension at 100° C. for 5 min. The particles were then washed threetimes with 200 ml sterile distilled H₂O by centrifugation at 2000×g for10 min, whereafter 185 mg of dried enzyme treated glucan was obtained.

The enzyme treatment will only cleave β-(1-6)-linkages withinβ-(1-6)-linked chains, but will not remove the β-(1-6)-linked glucosylresidue extending from the branching points. The resulting enzymetreated glucan can be characterized as a branched β-(1-3)-glucan withβ-(1-3)-linked sidechains being attached by a β-(1-6)-linkage and beingessentially free of β-(1-6)-linked chains.

EXAMPLE 3

This example provides the protocol to solubilize glucan particlesprepared in accordance with Example 1 by hydrolysis using formic acid(HCOOH).

2.0 g of glucan particles were suspended in 1.0 l of 90% formic acid andheated at 80° C. for 45 min under constant stirring. The suspension wascooled to 35° C. and the formic acid was evaporated. The residuecontaining the hydrolysed particles was boiled in 500 ml distilled waterfor 3 h, whereafter the cooled suspension was filtrated through a 0.44μm filter, frozen and lyophilized whereby 1.9 g of dry solubilizedparticles were obtained. The lyophilized solubilized particles were thendissolved in 100 ml distilled water and dialyzed, using a tubulardialysis membrane having a nominal molecular weight cut off (NMWCO) of5000 Dalton, against tap water for 24 h, and then lyophilized. Thisresulted in 1.8 g solubilized glucan product.

EXAMPLE 4

This example demonstrates the biological effects of glucan particlesprepared according to Example 1, and β-(1-6)-glucanase treated glucanparticles prepared according to Example 2 on immune responses inAtlantic salmon.

An A-layer positive isolate of Aeromonas salmonicida subsp. salmonicida,referred to as strain no. 3175/88 (Vikan Veterinary Fish ResearchStation, Namsos, Norway) was used. The bacterium was grown in brainheart infusion broth (Difco, USA) for 30 h at 14° C. in a shakerincubator, and the culture medium with the bacterium was centrifuged for10 min at 3000×g. The pellet was resuspended in 0.9% saline, and thebacterium was killed by adding 0.5% formalin (v/v) to the suspension andincubating at 14° C. for 24 h. The formalinized culture was then washedwith sterile 0.9% saline and resuspended to a concentration of 2×10⁹ml⁻¹ bacteria in 0.9% saline with 0.3% formalin. Bacterial suspensionswere mixed with an equal volume of saline or with the different glucansuspensions (10 mg ml⁻¹ in saline). Formalin was added to the vaccinesto a final concentration of 0.3% (v/v).

In carrying out these experiments, two groups of experimental fish wereused. In the vaccine experiment, Atlantic salmon presmolts of 20-40 gwere used. In the experiment where serum was collected for measuringblood lysozyme activity after glucan injection, Atlantic salmons of50-70 g were used. The fish were kept in 150 l tanks supplied withaerated fresh water at 12° C. and fed with commercial pellets ad libitumtwice daily.

In the vaccination experiment 40 fish in each group were IP-injectedwith 0.1 ml of the different vaccine preparations or vaccine withoutglucan as a control. Blood was collected in evacuated tubes (Venoject,Terumo-Europe, Belgium) from 10 fish in each group 6, 10, and 18 weeksafter injection. Blood samples were allowed to clot overnight at 4° C.and sera were collected after centrifuging the tubes at 2000×g for 10min. Individual serum samples were transferred to Micronic serum tubes(Flow Laboratories Ltd., Lugano, Switzerland) and stored at −80° C.until required.

In order to measure the effect of glucans on blood lysozyme activity,salmons were IP injected with 0.3 ml of the different glucans in salineor with 0.3 ml saline as the negative control. The glucans wereadministered at a concentration of 10 mg ml⁻¹. Blood samples werecollected from 10 fish from each group 10 and 20 days after injection,using evacuated tubes (Venoject). The tubes were kept on ice untilcentrifuged at 2000×g for 10 min, and individual serum samples weretransferred to Micronic serum tubes and stored at −80° C. untilrequired.

Lysozyme activity was measured with the turbidimetric method using 0.2mg ml⁻¹ lyophilized Micrococcus lvsodeikticus as the substrate in 0.04 Msodium phosphate buffer at pH 5.75. Serum (20 μl) was added to 3 ml ofthe suspension and the reduction in absorbance at 540 nm was measuredafter 0.5 min and 4.5 min at 22° C. One unit of lysozyme activity wasdefined as a reduction in absorbance of 0.001 min⁻¹. Results areexpressed as mean lysozyme activity in serum from 10 fish (Tables 1 and2).

The level of specific antibody against the A-layer of A. salmo-nicida insalmon sera was measured by an enzyme-linked immunosorbent assay(ELISA). A-layer protein was purified from whole A. salmonicida cells(Bjørnsdottir et al. (1992), Journal of Fish Diseases, 15:105-118), andprotein content was determined (Bradford, M. M. (1976), AnalyticalBiochemistry, 72:248-254) using a dye-reagent concentrate from Bio-RadLaboratories (Richmont, USA). Microtitre plates were coated with 100 μlof 5 μg ml⁻¹ A-layer protein in 50 mM carbonate buffer, pH 9.6, andincubated overnight at 4° C. The further procedure was performed asdescribed by H{dot over (a)}vardstein et al. (Journal of Fish Diseases(1990), 13:101-111). The antibody titre in pooled serum samples wasdetermined before individual serum samples were measured at threedifferent dilutions (1:500, 1:1000 and 1:2000). Absorbance was read at492 nm in a Multiscan MCC/340 MK II (Flow Laboratories Ltd). Results areexpressed as mean antibody response to the A-layer of the bacterium at adilution of 1:2000 in serum from 10 fish (Tables 1 and 2). TABLE 1Differences in biological effects of glucan particles and β- (1- 6)-glucanase treated glucan particles on immune responses in Atlanticsalmon. β- (1,6) -glucanase Saline Untreated glucan treated glucancontrol particles particles Lysozvme activity post injection (units/ml)10 days 304 505 529 20 days 330 407 454 Vaccine with β Vaccine Vaccinewith (1,6) -glucanase without untreated treated glucan glucan glucanparticles particles Antibody response post injection (absorbance)  6weeks 0.165 0.255 0.376 10 weeks 0.059 0.355 0.500 18 weeks 0.037 0.1970.142

Both injection of untreated and β-(1,6)-glucanase treated glucanparticles induced significantly higher (p<0.01) lysozyme activity inserum compared to saline control both 10 and 20 days post injection. Atday 20 post injection the lysozyme levels in fish injected withβ-(1,6)-glucanase treated glucan particles were significantly higher(p<0.05) compared to fish injected with untreated particles.

β-(1,6)-glucanase treated glucan particles induced significantly higher(p<0.05) antibody response to the vaccine compared to vaccine withoutadjuvant at all three sampling times, whereas untreated glucan particlesinduced significantly higher response 10 and 18 weeks post injection.β-(1,6)-glucanase treated glucan particles induced significantly higher(p<0.05) antibody response than did untreated glucan particles at 10weeks post injection, whereas no significant differences between the twowere observed at 6 and 18 weeks post injection. TABLE 2 Biologicaleffects of glucan particles and solubilized glucan. Solubilized SalineUntreated glu- glucan control can particles particles Lysozyme activity(units/ml) 10 days after 304 505 603 injection 20 days after 330 407 773injection Vaccine with Vaccine Vaccine with solubilized withoutuntreated glu- glucan glucan can particles particles Adjuvant effect(absorbance)  6 weeks after 0.165 0.255 0.184 injection 10 weeks after0.059 0.355 0.349 injection 18 weeks after 0.037 0.197 0.120 injection

Injection of solubilized glucan particles induced significant higher(p<0.01) lysozyme activity than did untreated glucan particles both 10and 20 days post injection. No significant differences could be observedbetween the ability of solubilized glucan particles and untreated glucanparticles to induce increased antibody response to the vaccine antigenat any sampling time point. Both induced significant higher (p<0.05)antibody response than vaccine without adjuvant 10 and 18 weeks postinjection, but not at 3 weeks post injection.

EXAMPLE 5

This example provides the protocol to obtain a glucan compositionsuitable for use in the feeding of animals.

1000 kg of dry cell wall material of Saccharomyces cerevisiae wassuspended in 5300 l of water at a temperature of 65° C. in a stainlesssteel tank. To the suspension of cell walls in water there was added 227l of 50% w/w NaOH so as to provide a caustic concentration of about 3%.The resulting mixture was then stirred for a period of about 4 h at atemperature of about 60° C.

Following the initial extraction period the suspension was then dilutedwith 8000 kg of water at a temperature of about 65° C. in a stainlesssteel, stirred, washing tank such that the weight of the mixture wasdoubled. The resulting diluted mixture was then maintained at atemperature of about 60° C. while being stirred for a period of about 15min. Thereafter the resulting mixed diluted suspension was centrifugedin a nozzle centrifuge (Alfa Laval DX209). The supernatant wasdiscarded. The resulting concentrated cell wall suspension wascontinuously introduced into a second steel stirred wash tank containing8000 kg water and the mixture adjusted by the addition of water to givea final weight of 0.14500 kg. The resulting suspension was then mixedfor a period of 15 min at a temperature of 60-65° C. Thereafter theagitated mixture was centrifuged.

The resulting cell wall suspension was continuously added to a thirdvessel containing 8000 kg water. Additional water at 60° C. was added toprovide a final weight of 14500 kg. The resulting suspension was stirredfor a period of 15 min at 60-65° C. and thereafter centrifuged.

Following centrifugation, the resulting cell wall concentrate wastransferred to a stainless steel storage tank wherein the suspension wascooled to a temperature of about 5-10° C. The resulting cooledsuspension was treated with phosphoric acid (H₃PO₄) in a stainless steelagitated tank in an amount to achieve a suspension of solids having a pHof 5.5-7.5.

Following neutralization the resulting neutralized mixture was subjectedto pasteurization by heating at a temperature of 75° C. for a period of18 seconds by passing the mixture through an in-line plate and frameheat exchanger.

Following pasteurization the resulting pasteurized mixture was thenspray dried in a spray drier maintained at an inlet air temperature ofat least 140-150° C. and an exhaust temperature of about 65-70° C.whereby there was achieved 300 kg of dry glucan product.

EXAMPLE 6

This example provides the protocol and effect of treatment of feed gradeglucan with a β-(1-6)-glucanase.

25 g of feed grade glucan, prepared in accordance with Example 5,suspended in 1.25 l of 50 mM sodium acetate, pH 5.0, in a 2 l conicalflask. Glucan particles were maintained in suspension by shaking, thesuspension was warmed to 30° C. and purified β-(1-6)-glucanase fromTrichoderma harzianum was added to a final concentration of 1.8 U/gglucan.

To follow the timecourse of the enzymatic removal of β-1,6-bound glucosefrom the glucan particle, 1 ml aliquotes of the suspension werewithdrawn at different timepoints, centrifuged at 2000×g, and 0.2 ml ofthe supernatants analyzed for free, reducing carbohydrate (Nelson et al.(1944), Journal of Biological Chemistry, 153:315-80). The glucansuspension was incubated for 28 h at which time the rate of release offree, reducing carbohydrate was observed to be very low. The glucanparticles were then pelleted by centrifugation at 2000×g, washed once in50 mM sodium-acetate, pH 5.0 and once in water.

A fine, dry powder suitable for use as a feed additive was prepared fromthe wet glucan by first dehydrating the pellet four times with ethanolat room temperature followed by air drying at room temperature.

Results from treating a feed grade glucan with β-(1-6)-glucanase from T.harzianum as described above are shown in Table 3. TABLE 3 Liberation ofglucose from feed grade glucan during treatment with β-(1-6) -glucanasefrom T. harzianum. Enzyme reaction Glucose liberated, time, (% of totalglucose in (h) glucan) 0 0.0 0.5 1.9 1 2.6 2 3.3 3 3.7 4 4.0 5 4.3 2 5.58 5.6

1. A branched β-(1,3) glucan with β-(1,3)-bound side chains beingattached by a β-(1,6)-linkage essentially free of β-(1,6)-linked chainshaving immunomodulatory effects
 2. The glucan according to claim 1prepared by contacting a branched β-(1,3)-glucan derived from yeasthaving β-(1.3)-linked side chains and β-(1,6) linked chains with aβ-(1,6)-glucanase.
 3. The glucan according to claim 1 wherein it isfurther solubilized.
 4. The glucan according to claim 3 wherein theglucan is produced by contacting the unsolubilized glucan with asolubilization agent.
 5. The solubilized glucan according to claim 4wherein said solubilization agent is formic acid.
 6. A branched β-(1,3)glucan with β-(1,3)-bound side chains being attached by a β-(1,6)linkage wherein the β-(1,6) linked chains do not contain more than fourβ-(1,6)-bound glucose units having immunomodulatory effects.
 7. Theglucan according to claim 6 prepared by contacting a branchedβ-(1,3)-glucan derived from yeast having β-(1.3)-linked side chains andβ-(1,6) linked chains with a β-(1,6)-glucanase.
 8. The glucan accordingto claim 6 wherein it is further solubilized
 9. The glucan according toclaim 8 wherein the glucan is produced by contacting the unsolubilizedglucan with a solubilization agent.
 10. The solubilized glucan accordingto claim 9 wherein said solubilization agent is formic acid.
 11. Animmunomodulatory composition comprising a branched β-(1,3) glucan withβ-(1,3)-bound side chains being attached by a β-(1,6)-linkageessentially free of β-(1,6)-linked chains.
 12. The glucan according toclaim 11 prepared by contacting a branched β-(1,3)-glucan derived fromyeast having β-(1,3)-linked side chains and β-(1,6) linked chains with aβ-(1,6)-glucanase.
 13. The glucan according to claim 11 wherein it isfurther solubilized.
 14. The glucan according to claim 13 wherein theglucan is produced by contacting the unsolubilized glucan with asolubilization agent.
 15. The solubilized glucan according to claim 14wherein said solubilization agent is formic acid.
 16. Animmunomodulatory composition comprising a branched β-(1,3) glucan withβ-(1,3)-bound side chains being attached by a β-(1,6) linkage whereinthe β(1,6) linked chains do not contain more than four β-(1,6)-boundglucose units.
 17. The glucan according to claim 16 prepared bycontacting a branched β-(1,3)-glucan derived from yeast havingβ-(1.3)-linked side chains and β-(1,6) linked chains with aβ-(1,6)-glucanase.
 18. The glucan according to claim 16 wherein it isfurther solubilized.
 19. The glucan according to claim 18 wherein theglucan is produced by contacting the unsolubilized glucan with asolubilization agent.
 20. The solubilized glucan according to claim 19wherein said solubilization agent is formic acid.
 21. A method ofincreasing immunostimulation in fish or mammals by administering to thefish or mammals a glucan product comprising a branched β-(1,3) glucanwith β-(1,3)-linked side chains being attached by a β-(1,6) linkageessentially free of β-(1,6)-linked chains.
 22. A method of increasingimmunostimulation in fish or mammals by administering to the fish ormammal a glucan product comprising a branched β-(1,3) glucan withβ-(1,3)-linked side chains being attached by β-(1,6)-linkage wherein theβ-(1,6) linked chains do not contain more than four β-(1,6)-boundglucose units.
 23. A method of preparing an insoluble glucan havingbranched β-(1,3) side chains being attached by a β-(1,6) linkageessentially free of β-(1,6) linked chains comprising the steps of: (a).contacting yeast cell walls with an aqueous alkaline solution undersuitable conditions to effect the extraction of proteins and lipidstherefrom; (b). separating the resulting extracted yeast cell walls fromsaid aqueous solution; (c). washing the resulting separate yeast cellsso as to further remove solubilized cell wall components therefrom; (d).neutralizing the washed yeast cell walls; and (e). pasteurizing theneutralized, washed cell walls and thereafter drying the resultingpasteurized neutralized, washed cell walls.
 24. A feed grade glucanprepared by the method according to claim
 23. 25. The method accordingto claim 23 wherein the glucan has β-(1,3) side chains being attached byβ-(1,6) linkage wherein the β-(1,6) linked side chains do not containmore than four β-(1,6)-bound glucose units.
 26. A feed grade glucanprepared by the method according to claim 25p.
 27. A solubilizedbranched β-(1,3)-glucan with β-(1,3)-bound side chains being attached bya β-(1,6)-linkage essentially free of β-(1,6)-linked chains containingmore than four β-(1,6) bound glucose units, wherein said glucan isproduced by contacting an unsolubilized glucan which is a branchedβ-(1,3)-glucan with β-(1,3)-bound side chains and which is attached viaa β-(1,6)-binding and which is free of β-(1,6)-bound chains, with asolubilization agent.
 28. The solubilized glucan according to claim 27wherein the solubilization agent is for formic acid.